Center brake for automobiles

ABSTRACT

A center brake for automobiles is disclosed. The brake has braking teeth (which may be triangular, trapezoidal or of other shape) formed on the outer surfaces of the brake shoes and on the inner surface of the brake drum for improved brake performance. Preferred brake drum material is cast iron and preferred brake shoe material is non-toxic to avoid health damage to those who come into contact with the brake. The mechanical structure of the preferred brake results in a system which reliably carries out its brake shoe return function even when there is a failure or malfunction of brake return springs or ice on the brake during cold weather. The preferred brake can be alternatively actuated by a switch or lever.

TECHNICAL FIELD

The present invention relates in general to center brakes, inparticular, for medium or large-sized automobiles such as trucks orbuses used for temporary parking of the automobile with the enginerunning or for reliably preventing a parked automobile from rolling whenthe engine is shut off.

BACKGROUND ART

It is well known to those skilled in the art that automobile brakes areused not only for reducing the speed of automobiles and stoppingautomobiles but also for preventing parked automobiles from rolling.Automobile brakes typically generate frictional force and convertkinetic energy of a moving automobile into thermal energy and evolve thethermal energy to the atmosphere, thereby providing a braking functionfor a moving automobile.

Typically, small-sized automobiles use two different types of brakes--afoot brake and a hand brake. A foot brake is for braking a movingautomobile in order to reduce the speed of or stop the automobile. Afoot brake is actuated by foot manipulation of a brake pedal. A handbrake (also called a side brake or parking brake) is for manuallybraking the rear wheels of the automobile in order to keep theautomobile stationary while it is parked. A hand brake is typicallyactuated by hand manipulation of a brake lever.

In contrast to the braking systems of small automobiles, medium andlarge automobiles such as trucks and buses also utilize a center brake.A center brake is typically a hand-operated brake which is adapted forbraking a propeller shaft (also called a drive shaft) of an automobile.On common truck designs with aforward-mounted engine and using rearwheel drive, power is transferred from the engine through a transmissionand then through an elongated propeller shaft or drive shaft connectedto the transmission and to the rear differential. The propeller shaft ordrive shaft is thus distinguished from an axle which transmits powerfrom the differential laterally to a wheel of the automobile.

Both center brakes and hand brakes are used for prevention of possibleslip or rolling of the automobile while it is parked on a slope. Thecenser brake is preferably used, in particular, when temporarily parkingthe automobile while leaving the engine running.

For example, fire engines or the fire trucks should be parked with theengine running when putting out afire. The engine of a fire truck shouldbe left running in order to provide water pumping force or power. Thegross weight of a fire truck carrying its load of water is very great.Consequently, a parked fire truck may be unstable and may tend to rollunder its own weight when the truck is braked by the hand brakeexclusively. Therefore, a center brake should be used in addition to ahand brake in order to securely brake and park a fire truck with theengine running.

However, there may be a problem when parking a fire truck with theengine running on a slope. That is, when the parking place of a firetruck is sloped, only a good center brake can reliably prevent the firetruck from moving. However, when the center brake of the fire truck isworn or malfunctioning, caused, for example, by abrasion of brakelining, the parked truck with the engine running and containing withmuch water may roll down the slope due to its great weight and may causea terrible accident.

Of course, the above problem caused by a worn or malfunctioning centerbrake may occur in other medium or large-sized automobiles, such as acargo truck or a bus, in addition to fire trucks.

Typically, brakes are classified into two types: drum brakes and diskbrakes. In a typical drum brake, two arcuate brake shoes fitted withheat and water-resistant linings are forced against an inner or outersurface of a rotating drum. A drum brake in which the shoes are forcedagainst the inner surface of the drum is referred to simply as aninternal forcing type brake. A drum brake in which the shoes are forcedagainst the outer surface of the drum is referred to simply as anexternal forcing brake. In a typical disk brake, disks attached to afixed frame are pressed, using hydraulic pressure, against disksattached to a rotating axle or against the inner surfaces of a rotatinghousing. In both disk and drum brakes, the linings or pads used asbraking means are typically made of asbestos which is noted to be veryinjurious to human health. In particular, asbestos is known to harm thefunction of hearts and lungs of users so that use of the asbestos forbrake linings or pads is undesirable. The above brakes have anotherproblem in that they do not achieve sufficiently great braking force,which is the object of brakes.

Still another problem of the above brakes is that the lining or pad ofthe brake is typically fixed to the brake shoe using a plurality ofrivets. Consequently, production of brakes is difficult and costly.Furthermore, it is noted that the brakes of consistent performance areseldom produced during mass production, resulting in brakes of varyingeffectiveness.

DISCLOSURE OF THE INVENTION

It is, therefore, a primary object of the present invention to provide acenter brake for automobiles in which the above problems can beovercome. The preferred brake includes a plurality of triangular ortrapezoidal braking teeth integrally formed on the outer surfaces of thebrake shoes and on the inner surface of the brake drum. When engaged,this structure provides perfect braking action and avoids the dangers ofunreliable brakes.

It is another object of the present invention to provide a center brakefor automobiles which does not use harmful material, such as asbestos,for the braking means. This provides a brake which does not causefunctional diseases of hearts and lungs of users and which does notcause environmental pollution.

It is still another object of the present invention to provide a centerbrake for automobiles which reliably carries out its brake shoe or brakemeans return action even if there is a malfunction of the return springsor if the brake components freeze during cold weather. This remarkablyimproves the operational reliability of the center brake.

It is a further object of the present invention to provide a centerbrake for automobiles which can be handled by a switch without handlinga lever when operating or releasing the center brake, thus to facilitateactuating the center brake.

In a preferred embodiment, the present invention provides a center brakefor automobiles comprising: a brake drum fixed to a propeller shaft(i.e., drive shaft) of the automobile and adapted for braking thepropeller shaft using frictional force generated by a pair of brakeshoes; a housing fitted to and closing the drum and used as a mount forvarieties of parts of the brake; a pair of brake shoes pivoted to thehousing by anchor pins such that the shoes are selectively turned abouttheir anchor pins by action of a cam and forced against the innersurface of the drum at a given frictional force; the cam being fixedlymounted to a shaft of an operating lever located at the top ends of theshoes and adapted for biasing the top ends of the shoes outward andopening the shoes in the drum, the operating lever being selectivelyoperated by a brake lever; a plurality of return springs for elasticallyreturning the operating lever and the shoes to their original positionswhen the brake lever is free from an actuating force; an adjusterdisposed between the bottom ends of the shoes and adapted forcontrolling a gap between the shoes; a compression coil spring extendingbetween he bottom ends of the shoes about the adjuster and adapted forpreventing separation of the adjuster from the shoes; and a plurality ofbraking teeth integrally formed on the inner surface of the drum and onthe outer surfaces of the shoes, the braking teeth of the shoes engagingwith the braking teeth of the drum during a braking action of the brake.

In another embodiment, the present invention provides a center brake forautomobiles comprising: a brake drum fixed to a propeller shaft of anautomobile and adapted for braking the propeller shaft using frictionalforce generated by a pair of brake shoes; a housing fitted to andclosing the drum and used as a mount for varieties of parts of thebrake; a pair of brake shoes disposed in the drum such that the shoesare moved outward and opened by action of a pair of cams and forcedagainst the inner surface of the drum at a given frictional force; thecams fixedly mounted to a shaft of an operating lever at ends of theshoes and adapted for biasing the ends of the shoes outward and foropening the shoes in the drum in order to force the shoes against theinner surface of the drum; a plurality of return springs for elasticallyreturning the shoes to their original positions when the brake lever isreleased; and a plurality of braking teeth integrally formed on theinner surface of the drum and on the outer surfaces of the shoes, thebraking teeth of the shoes engaging with the braking teeth of the drumduring a braking action of the brake.

The center brake of this invention provides a perfect braking action andensures a parked automobile will not roll under its own weight. Thepreferred brake materials do not cause functional diseases of hearts andlungs of users and do not cause environmental pollution. The preferredbrake structure provides a reliable return motion of the brake shoes andfacilitates handling of the brake.

BRIEF DESCRIPTION OF DRAWINGS

The above and other objects, features and other advantages of thepresent invention will be more clearly understood from the followingdetailed description taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 is an exploded perspective view of a center brake in accordancewith a preferred embodiment of the present invention;

FIG. 2 is a front view of the center brake of Fib. 1, after assemblingthe parts of the brake;

FIGS. 3A and 3B are partially enlarged views of center brakes of apreferred embodiment of the invention respectively, in which:

FIG. 3A shows the center brake having a plurality of triangular brakingteeth formed on the brake shoes and on the brake drum; and

FIG. 3B shows the center brake having a plurality of trapezoidal brakingteeth formed on the brake shoe and on the brake drum;

FIGS. 4A and 4B are sectional views showing operation of the internalforcing brake (the brake being of the single action type and using twoleading shoes) having triangular braking teeth of the invention;

FIGS. 5A and 5B are sectional views showing operation of an internalforcing brake (having a pair of double action shoes that are bothleading shoes) in accordance with another embodiment of the invention;

FIG. 6 is a partial view of the center brake provided with an airbooster or solenoid used as return means in accordance with theinvention; and

FIG. 7 is a partial view of the center brake provided with a solenoidand air booster used as braking means and return means of the brake,respectively, in accordance with the invention.

BEST MODE FOR CARRYING OUT THE INVENTION

With reference to FIGS. 1 and 2, there is shown a center brake forautomobiles in accordance with a primary embodiment of the presentinvention.

As shown in the drawings, a center brake of the invention is depicted.

The preferred center brake is of the internal forcing type (i.e., itforces brake shoes from an inward to an outward position to cause abraking action). The preferred brake includes a brake drum 10, whichdrum 10 is directly fixed to a propeller shaft or drive shaft (notshown) of an automobile. A propellor shaft or drive shaft isdistinguished from an axle shaft in that a propellor shaft typicallytransmits power from a transmission to a differential of an automobile,while an axle shaft typically transfers power from a differential of anautomobile to its wheel. The brake drum 10 is adapted for braking thepropeller shaft by using frictional force generated by a pair of brakeshoes 31. The drum 10 is fitted to and closed by or against a housing20. The housing 20 forms an internal space between it and the drum 10,which will be occupied by brake shoes 31 and other parts. Housing 20 isused as a mount or mounting plate on which varieties of parts of thebrake can be mounted or attached. The brake also includes a pair ofshoes 31. The brake depicted uses single action shoes (i.e., the shoesare driven toward the drum at only one of their ends), and the brake isof the two-leading shoes type (i.e., both shoes, as opposed to only asingle shoe, are directly driven toward the drum by an actuating force).The shoes 31 are provided, on their outer surfaces, with braking teeth311. The shoes 31 are pivotable with respect to the housing 20 by theiranchor pins 21 such that the shoes 31 are selectively turned about theiranchor pins 21 by action of a cam 40 and forced against the toothedinner surface of the drum 10 at a given frictional force. The cam 40 isfixedly mounted to a shaft of an operating lever 60 at the top ends ofthe shoes 31, thus to bias the top ends of the shoes 31 outward and toopen the shoes 31 within the drum 10 in order to cause the shoes 31 tobe forced against the inner surface of the drum 10. The operating lever60 is selectively operated by a brake lever. The brake also includes aplurality of return springs 50 which are provided both for the operatinglever 60 and for the shoes 31 and which are adapted for elasticallyreturning the operating lever 60 and the shoes 31 to their originalpositions when the brake lever (such as a flexible wire) is free fromactivating force. In the brake of this invention, the gap between theshoes 31 can be adjusted by a gap adjuster 70, which adjuster 70 isdisposed between the bottom ends of the shoes 31. A compression coilspring 55 is connected between the bottom ends of the shoes 31 adjacentthe adjuster 70 and prevents possible sudden separation of the adjuster70 from the shoes 31.

In the above center brake, the inner surface of the drum 10 and theouter surface of each shoe 31 are provided with triangular ortrapezoidal braking teeth 11 and 311, which teeth 11 and 311 areintegrally formed on their associated surfaces of the drum 10 and of theshoe 31. In this primary embodiment, the braking teeth 311 of the shoes31 are partially formed on the outer surfaces of the shoes 31 such thatthe teeth 311 are exclusively formed in a portion of each shoe 31 from aturning center of each shoe 31 to about the top end or the cam contactend of the shoe 31. The center brake further includes a pair ofconnectors 80 which connect the opposed ends of the cam 40 to the topends of the shoes 31 respectively. The connectors 80 are adapted forsmoothing the returning motion for the shoes 31 when releasing thebrake.

As shown in FIG. 6, an air booster 91 or a solenoid 92 is provided asmeans for forcibly returning the operating lever 60, the cam 40, and theshoes 31 to their original positions.

Please note that the air booster 91 may be preferably used as theforcible returning means for a brake for a large automobile, while asolenoid 92 is preferably used as the forcible returning means for abrake used in a small or medium-sized automobile.

FIG. 7 shows the braking means and the returning means of the inventedcenter brake in accordance with another embodiment of the invention. Inthis embodiment, the operating lever 60 is provided with both aswitch-operated one touch solenoid 91 used as the braking means, and anair booster 92 used as the returning means. The air booster 92 issupplied with air at the same time of release of the one touch solenoid91, thus to return the operating lever 60, the cam 40 and the shoes 31to their original positions and to release the center brake.

The present invention may be adapted for use in an internal forcingcenter brake having a pair of double-action (i.e., both the top and thebottom of the leading shoes are forced toward the drum by an activatingforce) two-leading shoes as shown in FIGS. 5A and 5B. In thisembodiment, the center brake includes a brake drum 10 which is directlyfixed to a propeller shaft of an automobile (not shown) and adapted forbraking the propeller shaft using frictional force generated by a pairof brake shoes 32. The drum 10 is fitted into and closed by or against ahousing 20. The housing 20 forms an internal space between it and thedrum 10 where the shoes 32 and other parts are located. Various parts ofthe brake are mounted to the housing 20. The brake also includes a pairof double-action two-leading shoes 32. The shoes 32 can be moved outwardand opened by action of a pair of cams 40 and forced against the innersurface of the drum 10 at a given frictional force. The cams 40 aremounted to a shaft of an operating lever 60 at the opposed ends of theshoes 32 (as depicted in the figure, the top end of each shoe 32 isactivated by a first cam and the bottom end of each shoe is activated bya second cam). The cams 40 bias the opposed ends of the shoes 32 outwardand to open the shoes 32 in the drum 10 in order to force the shoes 32against the inner surface of the drum 10. The brake also includes aplurality of return springs 50 which are provided for the operatinglever 60 and for the shoes 32 and which are adapted for elasticallyreturning the operating lever 60 and the shoes 32 to their originalpositions when the brake lever (such as a flexible wire) is released. Inthis center brake, the inner surface of the drum 10 and the outersurface of each shoe 32 are provided with triangular or trapezoidalbraking teeth 11 and 321, which teeth 11 and 321 are integrally formedon their associated surfaces. In contrast to the preferred embodiment ofFIGS. 4A and 4B, the braking teeth 321 of the shoes 32 of thisembodiment are nearly totally formed on the outer surfaces of the shoes32.

The operational effect of the center brake of the invention will begiven hereinbelow.

When forming the drum 10 and the single-action two-leading shoes 31 ofthe center brake according to the preferred embodiment of the invention,the braking teeth 11 and 311 are integrally formed, using given molds,on the inner surface of the drum 10 and on the outer surfaces of theshoes 31 respectively.

In contrast to typical center brakes, the center brake of this inventionhas no lining on the outer surfaces of the shoes but has the triangularor trapezoidal braking teeth 11 and 311 integrally formed on the innersurface of the drum 10 and on the outer surfaces of the shoes 31. Thebraking teeth 11 and 311 are preferably made of cast iron. With thebraking teeth 11 and 311, the brake of this invention is free frompost-machining and remarkably saves manufacturing cost and simplifiesassembly and disassembly of the center brake.

In the present invention, the braking teeth 11 and 311 have either thetriangular shape or the trapezoidal shape as shown in FIGS. 3A and 3B.Please note that it is preferred to use braking teeth 11 and 311 for asmall or medium-sized automobile that have the triangular shape of FIG.3A, while it is preferred to use braking teeth 11 and 311 for a largeautomobile that have the trapezoidal shape of FIG. 3B, as teeth withtrapezoidal shape an achieve stronger tooth-engaging force and therebyprovide a more secure braking action.

The single-action two-leading shoes 31 of the center brake are pivotablewith respect to the housing 20 about their anchor pins 21 andselectively turnable about their anchor pins 21 by action of the cam 40and are thereby forced against the inner surface of the drum 10. In thiscase, the braking teeth 311 of the shoes 31 come into engagement withthe teeth 11 of the drum 10 in such a manner that the tooth engagementbetween the teeth 11 and 311 starts at the teeth 311 about the anchorpins 21. Therefore, when the teeth 311 are totally formed on the outersurfaces of the shoes 31, the teeth 311 about the top ends of the shoes31 will not firmly engage with the teeth 11 of the drum, and will tendto slip off of teeth 11, reducing the effective braking force of thecenter brake. Furthermore, when the braking teeth 311 are totally formedon the outer surfaces of the shoes 31, the teeth 311 come into forcibleengagement with the teeth 11 so that the brake cannot achieve desiredsmooth returning motion of the shoes 31 when releasing the brake.

In order to resolve the above possible problem, the teeth 311 of eachshoe 31 are partially formed on the outer surface of the shoe 31 withinthe range from the turning center of each shoe to the top end of theshoe. In addition, the thickness of the teeth 311 gradually increases inthe direction from the turning center to the top end of each shoe 31.The teeth 311 of the shoes 31 thus substantially meet with the teeth 11of the drum of the drum 10 as shown in FIG. 4B when the shoes 31 areopened outward by the cam 40.

The center brake having single-action two-leading shoes 31 according tothe invention achieves the invented desired brake function for brakingthe propeller shaft of the automobile.

The center brake includes the connectors 80 which connect the opposedends of the cam 40, fixed to the operating lever 60, to the top ends ofthe shoes 31 respectively. As the connectors 80 pull the shoes 31 whenthe cam 40 returns to its original position in response to releasing ofthe brake, this brake achieves a smoother return motion of the shoes 31in comparison with typical brakes having no means for connecting the cam40 to the shoes 31.

The operating lever 60 of the center brake is provided with a solenoid91 or air booster 92, as shown in FIG. 6. This is in consideration ofpossible malfunction of the return springs 50 and possible freezing ofthe interface between the shoes 31 and the drum 10 in the winter. Thesolenoid 91 or air booster 92 ensures return of the shoes 31 when thecenter brake is released. When releasing the brake in the case ofmalfunction of the springs 50 or of freezing of the interface, the airbooster 92 or the solenoid 91 forcibly turns the operating lever 60,thus to cause return of the cam 40 and the shoes 31, both cooperatingwith the lever 60, to their original positions. Therefore, this centerbrake can be reliably released even in the case of malfunction of thesprings 50 or of freezing of the interface between the drum 10 and theshoes 31 in the winter.

The air booster 92 is operated by the air exclusively applied theretowhen the engine is running, and provides such a large amount of forcethat the booster 92 is preferably used in a brake for a largeautomobile. Meanwhile, the solenoid 91 is operated by a switch andpreferred to be used in a brake for small or medium-sized automobiles.

The solenoid 91 is a one touch solenoid. When the solenoid 91 is turnedon and operated once, the solenoid 91 can maintain its previous stateeven when the engine is turned off. The solenoid 91 having been kept inits previous state, returns to its original position at the same timethat power is turned off when the engine is running and the switch isturned off by the driver releasing the center brake.

FIG. 7 shows the braking means and the returning means of the centerbrake in accordance with another embodiment of the invention. In thisembodiment, the switch-operated one touch solenoid 91 used as thebraking means is coupled to a side of the operating lever 60, while theair booster 92 used as the returning means is coupled to the other sideof the operating lever 60. The solenoid 91 is turned on in response toswitch operation, thus to actuate the braking operation of the centerbrake. When the air booster 92 is operated when the solenoid 91 isturned off, it reliably returns the operating lever 60, the cam 40 andthe shoes 31 to their original positions.

When the switch-operated one touch solenoid 91 and the air booster 92are used as the braking means and the returning means of the centerbrake as described above, the center brake does not need to be operatedby the brake lever but is simply operated by switch operation so that itis possible to facilitate operation of the brake.

Turning to FIGS. 4A and 4B, there is shown operation of the center brakehaving single-action two-leading shoes 31 of the invention. As shown inthe drawings, when the brake is released, the arcuate two leading shoes31 in the brake drum 10 are biased inward by the spring force of thereturn springs 50 and turned inward about their anchor pins 21, thus tobe closed as shown in FIG. 4A.

In this case, there is a gap between the braking teeth 11 of the drum10, fixed to the propeller shaft of the automobile, and the teeth 311 ofthe shoes 31 so that the propeller shaft is applied with no brakingforce but can freely rotate.

When the brake lever or the switch (not shown) is actuated in order tobrake and stop the automobile, the operating lever 60 which is pivotedto the housing 20 and biased by the return spring 50 is forcibly turnedat a given turning angle in the direction of arrow of FIG. 4A.Therefore, the cam 40 fixed to the operating lever 60 is also turnedclockwise or in the turning direction of the lever 60.

The two-leading shoes 31, contacting the cam 40 at their top ends, arethus turned outward about their anchor pins 21 by the clockwise turningmotion of the cam 40, and are thus opened in the drum 10. Hence, thebraking teeth 311 of the shoes 31 come into engagement with the brakingteeth 11 of the drum 10 as shown in FIG. 4B.

When the teeth 311 of the shoes 31 substantially engage with the teeth11 of the drum 10 as shown in FIG. 4B, there is no slip between theshoes 31 and the drum 10. Thus, with this center brake can be stablybraked. In this regard, the center brake of the invention preventspossible safety accident caused by bad braking action of the brake.

In the center brake of this invention, the braking teeth 11 and 311 madeof cast iron have excellent durability in comparison with typical priorart brake linings made of asbestos. The teeth 11 and 311 will seldomwear at all and do not lose their braking function regardless of howlong they are used. Therefore, the center brake of this invention can beused indefinitely.

When the brake lever or the switch is handled in order to release thebrake, the solenoid 91 or the air booster 92 may be used as a returnmeans. The return function causes the arcuate two leading shoes 31 inthe brake drum 10 to be biased inward by the spring force of the returnsprings 50 and thus turned inward about their anchor pins 21, causingthem to be closed as shown in FIG. 4A and to thereby release thepropeller shaft of the automobile.

Of course, the present invention may be adapted for an internal forcingcenter brake having the double-action two-leading shoes 32 as shown inFIGS. 5A and 5B. In this case, the center brake will achieve the sameoperational effect as described for a brake having the single-actiontwo-leading shoes 31.

As the single-action two-leading shoes 32 are evenly biased outward byturning motion of the pair of cams 40 contacting the opposed ends of theshoes 32, braking teeth 321 each of equal thickness should be nearlytotally formed on the outer surfaces of the shoes 32. This is differentfrom the teeth 311 of the shoes 31 of the primary embodiment.

In this second embodiment, the braking teeth 11 of the drum 10 and thebraking teeth 321 of the shoes 32 may have either the triangular shapeor the trapezoidal shape in the same manner as described for the primaryembodiment having the single-action two-leading shoes 31.

The center brake of the second embodiment also has a pair of connectors80 for connecting the opposed ends of each cam 40 to their associatedends of the shoes 32. The connectors 80 are adapted to provide a smoothreturn motion of the shoes 32. In the same manner as described for theprimary embodiment, the center brake of this second embodiment mayinclude a solenoid 91 or an air booster 92 which will be used as thereturn means for the brake as shown in FIG. 6. Of course, it should beunderstood that the brake may be provided with a solenoid 91 and an airbooster 92 which will be used to actuate the braking means and torelease the brake, respectively, of the brake as shown in FIG. 7.

FIGS. 5A and 5B show operation of a center brake of the invention havingdouble-action two-leading shoes 32. The operation of this brake is thesame as brakes discussed above which use shoes 31, except for thedirection of movement of the shoes 32.

In contrast to typical center brakes having asbestos linings, the centerbrake of the invention having cast iron braking teeth 11, 311, 321reliably holds an automobile in place and does not allow it to rolluntil the brake is released. In this regard, the center brake preventspossible abrasion of the brake due to unskilled handling of the brakelever.

INDUSTRIAL APPLICABILITY

As described above, the present invention provides a center brake forautomobiles which is provided with a plurality of triangular ortrapezoidal braking teeth integrally formed on the outer surfaces of thebrake shoes and on the inner surface of the brake drum, thus to provideperfect braking action of the center brake and to prevent possiblesafety problems caused by ineffective prior art brakes.

The invented center brake does not use harmful materials, such asasbestos. Instead, steel is used as the braking means, thus preventingthe braking means not only from causing disease to users, but alsoavoids causing environmental pollution.

The invented center brake includes an air booster or a solenoid andreliably carries out its brakeshoe return function even if the brakefreezes during the winter, thus remarkably improving the reliability ofthe center brake.

The instant center brake can be actuated by a switch without use ofbrake lever when operating or releasing the center brake, thus tofacilitate use of the brake.

Although the preferred embodiments of the present invention have beendisclosed for illustrative purposes, those skilled in the art willappreciate that various modifications, additions and substitutions arepossible, without departing from the scope and spirit of the inventionas disclosed in the accompanying claims.

I claim:
 1. A center brake for automobiles comprising:a brake drum fixedto a drive shaft of the automobile, the brake drum being adapted forbraking the drive shaft using frictional force generated by a pair ofbrake shoes when the brake is engaged, a housing which said brake drummay be installed to, the combination of housing and brake drum creatingan enclosure in which brake parts may be located, a pair of brake shoesinstalled on said housing by use of anchor pins, each of said brakeshoes having a first end and a second end, said brake shoes beingcapable of pivoting with respect to said housing about said anchor pinswhen said brake shoes are forced against the inner surface of said brakedrum by an actuating force when the brake is engaged, a cam located onsaid housing, said cam being capable of exerting an actuating force onsaid brake shoes when the brake is engaged, the cam thereby biasing saidbrake shoes outward so that they pivot about their anchor pins andcontact the inner surface of said brake drum, an operating leverattached to said cam and being capable of effecting actuation of saidcam, a plurality of return springs for elastically returning saidoperating lever and said brake shoes to their original positions whensaid brake is disengaged, an adjuster disposed between said second endsof said brake shoes, said adjuster being adapted for controlling a gapbetween said brake shoes, a compression coil spring extending betweensaid second ends of said brake shoes proximate to said adjuster andadapted to prevent separation of said adjuster from said brake shoes,and a plurality of braking teeth integrally formed on the inner surfaceof said drum and on the outer surfaces of said shoes, the braking teethof said shoes engaging with the braking teeth of said drum when thebrake is engaged; wherein actuation of said brake shoes by said camcauses said brake shoes to come into contact with and firmly engage saidbrake drum with the interior surface of said brake drum when the brakeis engaged.
 2. The center brake recited in claim 1,wherein said anchorpins define a turning center for each of said brake shoes, the turningcenter being the point about which said brake shoes turn when the brakeis engaged; and wherein said braking teeth of said brake shoes areformed on the outer surfaces of said brake shoes from about said turningcenters of said brake shoes to about said first ends of said brakeshoes.
 3. The center brake recited in claim 1,wherein said braking teethof said brake shoes and said braking teeth of said brake drum aretriangular in shape.
 4. The center brake recited in claim 1,wherein saidbraking teeth of said brake shoes and said braking teeth of said brakedrum are trapezoidal in shape.
 5. The center brake recited in claim 1,further comprising:a pair of connectors for connecting said cam to saidfirst ends of said brake shoes; wherein said connectors are adapted toprovide a smooth return motion of said brake shoes when the brake isdisengaged.
 6. The center brake recited in claim 1, furthercomprising:an air booster coupled to said operating lever; wherein saidair booster is adapted to forcibly return said operating lever, said camand said brake shoes to their original positions when the brake isdisengaged.
 7. The center brake recited in claim 1, further comprising:asolenoid coupled to said operating lever; wherein said solenoid isadapted to forcibly return said operating lever, said cam and said brakeshoes to their original positions when the brake is disengaged.
 8. Thecenter brake recited in claim 1, further comprising:a solenoid coupledto said operating lever, said solenoid being capable of engaging thebrake by operating said operating lever, and an air booster coupled tosaid operating lever, said air booster being capable of disengaging thebrake, said air booster being configured to be supplied with air whensaid solenoid is turned off, thereby effecting brake disengagement byforcibly returning said operating lever, cam and brake shoes to theiroriginal positions.
 9. A center brake for automobiles comprising:a brakedrum fixed to a drive shaft of an automobile and adapted for braking thedrive shaft by using frictional force generated by a pair of brakeshoes, a housing against which said brake drum may be installed, thecombination of brake drum and housing forming an enclosure in whichbrake parts may be located, and said housing forming a mounting locationwhere brake parts may be installed, a pair of brake shoes disposed insaid brake drum, each of said brake shoes having a first end and asecond end, said brake shoe first ends being adjacent each other in theassembled brake, and said brake shoe second ends being adjacent eachother in the assembled brake, an operating lever, a first cam and asecond cam installed to be actuated by said operating lever, said firstcam being installed in said enclosure between said brake shoe firstends, and said second cam being installed in said enclosure between saidbrake shoe second ends, a plurality of return springs being capable ofelastically returning said brake shoes to their original positions whenthe brake is disengaged, and a plurality of braking teeth integrallyformed on the inner surface of said drum and on the outer surfaces ofsaid brake shoes, the braking teeth of said brake shoes engaging thebraking teeth of said brake drum when the brake is engaged.